The present invention relates to a method of repairing an existing section of concrete slab which has had portions settle into the ground so as to become uneven over time. More specifically, to a method of carefully raising a section of settled cement slab so as not to damage the section and allow for the injection of pressurized mason's sand into the cavity created between the bottom of the uneven cement slab and the settled ground.
Regardless of the care and skill used in the initial construction, concrete slabs tend to become misaligned over time due to different rates of settlement of the earth. Uplift from freeze/thaw cycles or tree root lifting are also common causes of slab misalignment. These problems cause cracks in the cement slab to develop and can also cause step-like structures to occur between sections of the slab. The end result of this condition is the creation of hazards to its users and liability for those who are responsible for their care. Additionally, the uneven cement slabs are extremely difficult to clear of snow and ice during the winter months in the northern areas of the United States, thus creating further hazards and liabilities for their users and owners.
In the past, there was a number of ways these problems were solved. One of these was to completely remove the damaged section of cement slab and then re-pour it. The problem with this method is that although it works very well, it is time consuming and very expensive. The re-pour method also results in a checkerboard looking cement slab as the new portions are often a very different color from the older weathered sections. Another method that has been used with the step formation problem is to construct concrete or tar ramps from the lower section of the cement slab to the upper. The problem with this method is that it still leaves uneven slab surfaces that are hazardous and difficult to maintain.
Finally, another method that is often used is mud jacking. In this repair method a hole is drilled through the uneven slab and wet mud is pumped under the slab until the slab becomes level. The first problem with this method is that the mud commonly used in this process is not viscous enough to provide an adequate amount of force to the cement slab to lift it enough to effectuate the repair. Another problem with the mud jacking method is that it requires that there be a substantial open area, or settle cavity, between the lower surface of the concrete slab on the underlying ground. Finally, the use of wet mud makes for an ineffectual repair as it tends to settle over time while drying resulting in a cement slab surface that retains the uneven condition that was intended to be repaired.
More recently, a number of patents have issued that attempt to deal with this problem in an effective and cost efficient manner. In U.S. Pat. No. 4,962,913, Stewart, Oct. 16, 1990, a method of lifting and repairing such damaged sidewalks is provided. The problem with this device is that by nature of its construction, a heavy frame supported by four wheels, it is large and cumbersome in operation. Further, this device requires the even lifting of a given slab in only small sections at a time, as one portion of the device rests on an un-lifted portion of the sidewalk. In U.S. Pat. No. 4,982,930, Stewart, Jan. 8, 1991, the same inventor attempted to resolve the short comings of his prior art by lightening the frame and removing the wheels. However, the resulting apparatus is still large and cumbersome in its operation. Additionally, these solutions are not capable of raising large sections of cement slabs and are therefore limited in their applications.
Therefore, from the foregoing discussion it can be seen that it would be desirable to provide a means of leveling existing cement slabs in an inexpensive manner that is highly portable, easily used and which also results in repaired slabs that are not subject to the settling problems that affect other repair methods. Furthermore, it can also be seen that it would be desirable to provide a method of repairing uneven sections of existing concrete slabs that would be capable of lifting large sections of the slabs in a manner that does not require mechanical heavy lifting apparatuses and that would be highly portable and capable of operating independently from outside power sources.